1. Field of the Invention
The present invention generally relates to multi-piece golf balls and more particularly to golf balls having at least one component made of a composition comprising a polymerized substituted imidazolium liquid ionomer. The multi-piece golf ball includes a core, which may be constructed of a center and surrounding outer core layer. Preferably at least one of the core layers is formed from a composition comprising a rubber material or highly neutralized acid copolymer and the liquid ionomer. The golf ball further includes a cover, which may be a dual-cover having inner and outer cover layers.
2. Brief Review of the Related Art
Today, both professional and amateur golfers use multi-piece solid golf balls. Basically, a two-piece solid golf ball includes a solid inner core protected by an outer cover. The inner core is made commonly of a rubber material such as natural and synthetic rubbers: styrene butadiene, polybutadiene, or polyisoprene. Highly neutralized ethylene acid copolymer ionomer resins (HNPs) also may be used to form the core. The outer cover is made commonly of thermoplastic or thermoset resins such as ionomers, polyolefins, polyamides, polyesters, polyurethanes, and polyureas. As new materials and manufacturing processes have become more economically feasible, three-piece, four-piece, and five-piece solid golf balls have been introduced. Different materials are used in the golf ball construction to impart specific properties and playing features to the ball.
For example, the resiliency and rebounding performance of a golf ball is based primarily on its core. Balls having a high resiliency tend to reach a high velocity when struck by a golf club. As a result, the ball tends to travel a greater distance. This helps the ball travel longer distances. In a majority of golf balls used today, conventional cores comprise polybutadiene rubber (“PBR”). The core construction may be single or multi-layered. That is, the golf ball may include a single core layer (center). In another version, the golf ball may have a dual-core construction comprising an inner core and at least one surrounding core layer. In yet another version, the golf ball may contain a multi-layered core comprising an inner core, intermediate core layer, and outer core layer. The PBR compositions typically contain “fillers,” which are added to adjust the density and/or specific gravity of the material. Adjusting the weight of the golf ball either towards the center or outer surface of the ball changes the flight and spin characteristics of the ball. In other golf ball constructions, highly neutralized polymers of ionomers (HNPs), particularly ionomers made of ethylene and a vinyl comonomer having an acid group such as methacrylic, acrylic acid, or maleic acid, are used to form a core layer. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the copolymer. Commercially available ethylene-based ionomer resins are available in various grades and identified based on type of base resin, molecular weight, and type of metal ion, amount of acid, degree of neutralization, additives, and other properties.
For example, Ohsumi et al., U.S. Pat. No. 5,772,531 discloses a multi-piece solid golf ball containing a core having a three-layered structure. A polybutadiene rubber is used as the base rubber for the inner and outer core layers. A thermoplastic resin, for example, an ionomer resin and a thermoplastic elastomer composed of styrene, olefin, urethane, ester, or amide is used as the base rubber for the intermediate core layer. The hardness of the inner and outer core layers (for example, 65 to 95 JIS-c) is greater than the hardness of the intermediate core layer (for example, 50 to 75 JIS-c).
Higuchi et al., U.S. Pat. Nos. 6,634,961 and 7,086,969 disclose multi-piece solid golf balls containing a solid core consisting of a center core and outer core, and cover material. The inner core and outer core layer are molded from rubber compositions comprising a base rubber (20 to 100 wt % of a polybutadiene); peroxide; 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane; zinc oxide; antioxidant; zinc acrylate; and zinc salt of pentachlorothiophenol. The base rubber may be blended with other diene rubbers including polybutadiene rubber, styrene-butadiene rubber (SBR), natural rubber, polyisoprene rubber, and ethylene-propylene-diene rubber (EPDM). In these multi-piece cores, the center core has a hardness (40 to 60 JIS-c) that is less than the surface hardness of the outer core (75 to 95 JIS-c).
Rajagopalan et al., U.S. Pat. No. 6,894,098 discloses golf balls containing cores made of highly-neutralized polymers (“HNPs”). The acid moieties of the HNPs are preferably neutralized greater than about 70%, more preferably greater than about 90%, and most preferably at least about 100%. The HNP composition also may contain organic fatty acids and a second polymer component such as ionomeric copolymers and terpolymers, ionomer precursors, thermoplastics, polyamides, polycarbonates, polyesters, polyurethanes, polyureas, thermoplastic elastomers, polybutadiene rubber, balata, metallocene-catalyzed polymers (grafted and non-grafted), single-site polymers, high-crystalline acid polymers, and cationic ionomers.
Voorheis et al., U.S. Pat. No. 7,148,279 discloses a golf ball having a core and a cover, wherein at least one of the core or the cover includes a blend of a highly neutralized ionomer formed from a reaction between an ionomer having acid groups, a suitable cation source, and a salt of an organic acid, the cation source being present in an amount sufficient to neutralized the acid by 80% or greater; and a cross-linked or vulcanized diene
Sullivan et al., U.S. Pat. No. 7,722,482 discloses a multi-layer core having a center and an outer core layer that are both soft relative to a hard intermediate core layer. The outer core layer is thin relative to the center and the outer core layer. The base rubber is preferably polybutadiene or a mixture of polybutadiene with lesser amounts of elastomers such as cis-polyisoprene, trans-polyisoprene, balata, polychloroprene, polynorbornene, polyoctenamer, polypentenamer, butyl rubber, ethylene-propylene rubber, ethylene-propylene diene rubber, and styrene-butadiene.
Sullivan et al., U.S. Pat. No. 7,874,939 discloses golf balls containing a multi-layered core. The inner core is formed of a composition comprising polybutadiene rubber, zinc diacrylate, an organic peroxide, and zinc oxide. The outer core is formed of a composition comprising polybutadiene rubber, a stiffening agent, zinc diacrylate, an organic peroxide, zinc oxide and barytes filler. The inner core has a hardness less than the hardness of the outer core and a specific gravity less than or equal to the outer core specific gravity.
The industry continues to look at new materials for constructing golf balls. For example, new rubber compositions that could be used to make golf ball cores would be desirable. It is recognized that any particulate matter contained in such compositions should be dispersed well. That is, the particulate matter should be dispersed highly to prevent particles from sticking together and forming aggregates. Good dispersion is important, because it means the material can be molded more easily into a golf ball core or other ball component. Dispersing aids may be used in the composition; provided, however, these aids do not destroy any beneficial properties of the composition. For example, as discussed above, the resiliency and rebounding performance of the golf ball is important. Highly resilient golf balls rebound faster, retain more total energy when struck with a club, and have longer flight distance. In addition, the compression and hardness of the core are significant. Any ingredient added to a core composition for improving dispersion should not be detrimental to resiliency or other performance properties. The present invention provides compositions having good dispersion and other advantageous properties that can be used to make golf ball cores and other ball components.